Conventional memories used in computers generally employ a method in which information stored in a memory is accessed by specifying the address corresponding to the location of the information in the memory. This type of memory device has a disadvantage in that data previously stored at a location may not be recovered once new information has been stored at the location and the data can only be accessed by specifying corresponding address regardless of the content of data stored therein. To solve this problem, associative memories have been developed wherein information is stored and searched on the basis of a reference input supplied from the outside. The reference input comprises part of the information stored or to be stored and all entries in the memory can be searched in one clock cycle.
Many associative memories have been developed and used as part of a computer memory, and are intended for storing electric digital signals. Such memories are formed as an electric integrated circuit. A scanning operation is necessitated when pattern information is involved, and this requires a much longer time in processing the data and large-scaled data processing in a parallel mode. It has been impossible to obtain outputs successively. Further, due to the fact that a number of arithmetic circuits are required, there may be difficulty in wiring among the circuits.